The carrier tape for packaging an electronic component such as IC and LSI in an electronic device is conventionally formed from a sheet comprising a vinyl chloride resin, a styrene-based resin or the like. For example, as for the styrene-based resin, a sheet obtained by mixing a general-purpose polystyrene resin and a styrene-butadiene block copolymer is used. In view of the form on use, the carrier tape is required to have a good balance of physical properties such as transparency, rigidity, impact resistance, bending resistance and shapability, and various studies have been heretofore made to enhance these properties and obtain a good balance thereof.
For example, Patent Document 1 discloses a styrene-based resin composition comprising a block copolymer comprising a vinyl aromatic hydrocarbon and a conjugated diene, a vinyl aromatic hydrocarbon-acrylic acid ester copolymer, and a rubber-modified impact-resistant polystyrene-based resin, for obtaining a styrene-based resin suitable for a transparent carrier tape excellent in the transparency, rigidity and impact resistance.
Patent Document 2 discloses an embossed carrier tape comprising an alloy of a polystyrene resin with a styrene-diene-based elastomer copolymer, for obtaining an embossed carrier tape free from generation of a problem such as whitening or cracking at the bending.
Patent Document 3 discloses a sheet which contains a polystyrene-based resin and a rubber-reinforced styrene-based resin on both surfaces of a substrate layer comprising a styrene-butadiene copolymer and a polystyrene-based resin, for obtaining a molded article for the transportation of an electronic component, which is formed of a sheet excellent in the buckling strength, impact resistance, rigidity, printing suitability and heat-sealing property.
Patent Document 4 discloses a sheet having a constitution such that an outer layer formed of a resin composition comprising a styrene-based resin and a styrene-butadiene block copolymer is provided on both surfaces of a substrate layer comprising a styrene-based thermoplastic elastomer and a styrene-based resin, for obtaining a styrene-based resin sheet excellent in the bending strength, buckling strength, impact resistance and rigidity, which comprises a plurality of resin layers integrally stacked and uniform in the thickness, and also for obtaining a molded article for the transportation of an electronic component, which is formed of the sheet.
Patent Document 5 discloses a sheet having a surface layer comprising a styrene-conjugated diene block copolymer and a styrene-based resin, on at least one surface of a substrate layer comprising a styrene-based resin or a styrene-conjugated diene block copolymer and a styrene-based resin, for obtaining a sheet excellent in the transparency, shapability and rigidity.
Patent Document 6 discloses a resin composition comprising a specific styrene-conjugated block copolymer and a polystyrene-based resin, and a sheet comprising the resin composition, for obtaining a resin composition and a sheet, which are excellent in the shapability and transparency.
Patent Document 7 discloses a resin composition comprising a rubber component-containing styrene-based resin and a styrene-conjugated diene block copolymer, and a sheet comprising the resin composition, for obtaining a resin composition suitable for electronic component packaging and excellent in the transparency, shapability and impact strength and also for obtaining a sheet using the same.
However, these resin compositions comprising a block copolymer which comprises a vinyl aromatic hydrocarbon and a conjugated diene, and a vinyl aromatic hydrocarbon-based polymer are insufficient in the thermal stability and balance of physical properties suitable for a carrier tape, such as rigidity, transparency, impact resistance and heat shrinkability, and a method for improving such a problem is not disclosed in those publications. The problem is still pointed out on the market.
Patent Document 1: JP-A-10-279755
Patent Document 2: JP-A-10-236576
Patent Document 3: JP-A-2002-113818
Patent Document 4: JP-A-2002-283502
Patent Document 5: JP-A-2002-331621
Patent Document 6: JP-A-2002-332392
Patent Document 7: JP-A-2003-55526